Posts Tagged ‘Digital’

I recently powered up my old DEC Vaxstation 4000/90 out of curiosity to see if it still worked and discovered that no, it didn’t. The fans in the power supply spun up, the noisy SCSI hard disk whirred and clicked into life but nothing else happened. Anyone familiar with these and similar DEC machines knows there’s a bank of eight diagnostic LED’s that provide error reporting as the machine initialises and tests its various bits of hardware. All eight were lit and weren’t changing, it looked dead.

A lot of machines of this era have what is known as a timekeeper chip which is some non-volatile RAM with a crystal and battery piggy-backed on top and encased in resin. It keeps time and the battery allows the RAM to retain its contents whilst the machine is powered off. The contents are usually important machine settings, such as which disk to boot from, etc.

The 4000/90 has a Dallas Semiconductor DS1287 which is a fairly ubiquitous part and the batteries in these chips are only supposed to last for about 10 years so given the 4000/90 was introduced in the early 1990’s, chances are by 2016 the battery is flat. Early Sun Microsystems machines are plagued with a similar problem however they tend to still power up, but then report bad values for their host ID, MAC address, etc.

There’s two possible fixes. One, fit a new timekeeper chip which given they’re not manufactured any longer may mean fitting a “new” chip that has sat on the shelf for a number of years and so the battery has already lost much of its charge. Alternatively, and what I ended up doing, is to add a new battery to the existing chip.

The first job is to locate and extract the chip. Here is the DS1287 fitted to the 4000/90:

Note the dot identifying pin 1. Thankfully it’s in a socket so with a bit of careful coercion it should come out. The next step is to use a dremel or file to grind away the plastic and resin above where pins 16 & 20 would normally be, (they’re still present but bent up inside the package and attached to the battery):

Using a multimeter across these two terminals showed there was only 220-230 mV left in the battery so it was almost flat. Now the battery needs to be disconnected by breaking the contact on pin 16 so that the multimeter shows no voltage when placed across the exposed contacts near the base of the chip. With that done add some small wires, soldering them to the same contacts with the aim of attaching them to a battery holder:

Then add the battery holder and battery; I used a standard CR2032 Lithium coin cell. The positive terminal goes to pin 20 and the negative terminal goes to pin 16. I also put some more hot glue over the exposed contacts:

Now reinstall the chip back into the 4000/90 taking care to both orientate it correctly and not bend any of the pins:

At this point it was time to try and power on the Vaxstation and this time it worked and emitted its little warble and dropped me to the SRM console:

It was a bit confused as it had lost all of its settings so didn’t know where to boot from, etc. but other than that seemed fine. After fixing this I figured my DEC 3000/600 Alpha might also have the same issue so powered that up to find yes it did, but it at least boots to the SRM console and reports an NVR (Non-Volative RAM) fault. Here’s the timekeeper chip hidden underneath the middle TURBOchannel expansion slot and bingo, it’s another DS1287:

I performed the exact same steps as before and refitted the modified chip:

The NVR fault has now disappeared. Both machines should now be good for another 10 years or so, although it’s likely the elderly hard disks will seize up, or maybe a capacitor in the power supply will leak.